The discussion of the background herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
It has been observed that some children focus inaccurately when they observe an object which is situated a short distance away, that is to say, in near vision conditions. Because of this focusing defect on the part of a myopic condition, a child corrected for far vision, has the image of an object close by formed behind his retina, even in the foveal area.
To avoid making a myopia progression, which is due to this focusing defect, a myopia-correcting lens is known to be used, which is of the progressive multifocal ophthalmic lens type. An example of such a progressive multifocal ophthalmic lens is disclosed in U.S. Pat. No. 6,343,861.
Such a progressive multifocal ophthalmic lens comprises a far vision area, in which the optical power of the lens is adapted to correct the myopia of the wearer when observing a far distant object, and a near vision area, in which the myopia correction is reduced, as well as an intermediate area, which is situated between the far vision and near vision areas, and in which the optical power of the lens varies continually. Such progressive multifocal ophthalmic lenses are adapted for the foveal vision of the weaver.
Nevertheless, it has been observed that such progressive multifocal ophthalmic lens may cause more aggravation of the ametropia of the wearer when not used properly.
Indeed, as children are not presbyopic, they do not require power to clearly see near objects and can, therefore, use any part of a progressive multifocal ophthalmic lens to read or write.
Using the far and near vision zones of a progressive multifocal ophthalmic lens provides good optical quality images while using intermediate vision may provide a lower optical quality image, because of narrow visual fields, resulting in rapidly increasing levels of aberrations as soon as the child turns their eyes away from the meridian line.
Providing lower optical quality images through the progressive multifocal ophthalmic lens increases myopia progression.
Moreover, it is known that the correction of myopia of a wearer of glasses results, in the long term, in an increase in the degree of myopia. Such an aggravation of the myopia is seen in particular in children.
Such an increase in the degree of myopia is attributed to an ophthalmic correction, which is adapted for the observation of a distant object by using the central part of the retina, but which is too great for lateral parts of this object, the images of which are formed in the peripheral area of the retina.
The foveal vision, or central vision, corresponds to the observation of the object with the central part of each retina, which is called the foveal area.
The lateral parts of the observed object, which are imaged by light rays entering obliquely into the eye, correspond to the peripheral vision of the wearer. Those skilled in the art then speak of overcorrection of the myopia in these peripheral vision conditions. In practice, by using ophthalmic lenses whose optical power is adapted for the far vision and the foveal vision, the image in far vision is formed on the retina in the foveal area, but behind the retina for the peripheral vision.
It is considered that such a peripheral defocusing causes an elongation of the eye and, consequently, an apparent aggravation of the myopia of the wearer.
U.S. Pat. No. 7,992,997 B2 discloses an ophthalmic lens element to slow the progression of myopia wherein the peripheral region provides an optical correction for retarding myopia, based on a more positive power, compared to the distance refraction of the wearer. Moreover, it includes near, far and intermediate zones of low surface astigmatism. FIG. 6 of this document describes an example where the astigmatism in those three zones is close to zero, or at least of equivalent astigmatism as described in FIG. 2 of this document by the iso line 202.
It therefore appears that the ophthalmic lens element disclosed in this document aims to have far, intermediate and near vision of equivalent low astigmatism.
U.S. Pat. No. 7,862,171 B2 discloses a lens to correct myopia wherein a peripheral zone of more relative positive power, surrounding the far vision zone, corrects the peripheral vision of the wearer. The lenses disclosed are not specifically progressive lenses. The examples described represent either rotational symmetrical lenses which do have a high astigmatism in intermediate vision (FIG. 2B of this document) but a power corresponding to near vision, which is lower than in the intermediate vision (FIG. 2A of this document), or rotational symmetrical lenses with increasing power between far and near vision (FIG. 6A of this document) but with high astigmatism in near vision, i.e., equivalent to an intermediate vision zone (FIG. 6B of this document).